Liquid crystal device

ABSTRACT

A liquid crystal device is formed by applying an alignment film comprising a fluorine-containing polyimide having a fluorine-containing substituent in its moiety originated from a diamine on at least one of a pair of substrates sandwiching a chiral smectic liquid crystal. Preferably, the respective substrates are provided with such fluorine-containing polyimide alignment films which have been rubbed in directions which are substantially parallel with each other and identical to each other or which intersect each other at a small counter-clockwise intersection angle. The liquid crystal device thus formed shows a high contrast display, particularly by multiplexing drive, free from after-image because of quick responsiveness.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to a liquid crystal device to be used in a liquidcrystal display device or a liquid crystal-optical shutter, etc.,particularly a liquid crystal device by use of a ferroelectric liquidcrystal, more particularly to a liquid crystal device improved indisplay characteristics through improvement in initial alignment of theliquid crystal molecules.

A display device of the type which controls transmission of light incombination with a polarizing device by utilizing the refractive indexanisotropy of ferroelectric liquid crystal molecules has been proposedby Clark and Lagerwall (Japanese Laid-Open Patent Application No.107216/1981, U.S. Pat. No. 4,367,924). The ferroelectric liquid crystalhas generally chiral smectic C phase (SmC*) of H phase (SmH*) of anon-helical structure and, under this state, shows a property of takingeither one of a first optically stable state and a second opticallystable state responding to an electrical field applied thereto andmaintaining such a state in the absence of an electrical field, namelybistability, and also has a rapid response to the change in electricalfield. Thus, it is expected to be utilized in a high speed and memorytype display device and particularly to provide a large-area,high-resolution display.

For an optical modulating device by use of a liquid crystal having suchbistability to exhibit desirable driving characteristics, it is requiredthat the liquid crystal disposed between a pair of substrates should bein such a molecular alignment state that conversion between the abovetwo stable states may occur effectively irrespective of the applicationof an electrical field.

Further, in a liquid crystal device utilizing birefringence of a liquidcrystal, the transmittance under right angle cross nicols is given bythe following equation:

    I/I.sub.0 =sin.sup.2 4θ·sin.sup.2 (Δnd/λ)π,

wherein

I₀ : incident light intensity,

I: transmitted light intensity,

θ: tilt angle,

Δn: refractive index anisotropy,

d: thickness of the liquid crystal layer,

λ: wavelength of the incident light.

The tilt angle θ in the above-mentioned non-helical structure isrecognized as a half of an angle between the average molecular axisdirections of liquid crystal molecules in a twisted alignment in a firstorientation state and a second orientation state. According to the aboveequation, it is shown that a tilt angle θ of 22.5 degrees provides amaximum transmittance and the tilt angle in a non-helical structure forrealizing bistability should desirably be as close as possible to 22.5degrees.

A method for aligning a ferroelectric liquid crystal should desirably besuch that molecular layers each composed of a plurality of molecules ofa smectic liquid crystal are aligned uniaxially along their normals, andit is desirable to accomplish such an alignment state by a rubbingtreatment which requires only a simple production step.

As an alignment method for a ferroelectric liquid crystal, particularlya chiral smectic liquid crystal in a non-helical structure, onedisclosed in U.S. Pat. No. 4,561,726 has been known for example.

However, when a conventional alignment method, particularly one using apolyimide film treated by rubbing, is applied for alignment of aferroelectric liquid crystal in a non-helical structure exhibitingbistability reported by Clark and Lagerwall, the following problems areencountered.

That is, according to our experiments, it has been found that a tiltangle θ (an angle shown in FIG. 3 as described below) in a ferroelectricliquid crystal with a non-helical structure obtained by alignment withan alignment control film of the prior art has become smaller ascompared with a tilt angle H (the angle H is a half of the apex angle ofthe cone shown in FIG. 2 as described below) in the ferroelectric liquidcrystal having a helical structure. Particularly, the tilt angle θ in aferroelectric liquid crystal with a non-helical structure obtained byalignment with alignment control films of the prior art was found to begenerally on the order of 3-8 degrees, and the transmittance at thattime was at most about 3 to 5%.

Thus, according to Clark and Lagerwall, the tilt angle in aferroelectric liquid crystal with a non-helical structure realizingbistability should have the same angle as the tilt angle in theferroelectric liquid crystal having a helical structure, but in fact thetilt angle θ in a non-helical structure is smaller than the tilt angle Hin a helical structure. More specifically, it has been found that thetilt angle θ in a non-helical structure becomes smaller than the tiltangle H because of a twist alignment of liquid crystal molecules in thenon-helical structure. Thus, in a ferroelectric liquid crystal having anon-helical structure, liquid crystal molecules are aligned with a twistfrom a molecular axis adjacent to an upper substrate to a molecular axisadjacent to a lower substrate continuously at a certain twist angle.This leads to a phenomenon that the tilt angle θ in the non-helicalstructure is smaller than the tilt angle H in the helical structure.

Further, in an alignment state of a chiral smectic liquid crystalattained by a conventional polyimide alignment film subjected to arubbing treatment, when a liquid crystal is supplied with a voltage ofone polarity for switching from a first optically stable state (e.g., awhite display state) to a second optically stable state (e.g., a blackdisplay state) and then the voltage of one polarity is removed, theferroelectric liquid crystal layer is supplied with a reverse electricfield Vrev due to the presence of the polyimide film as an insulatinglayer between the electrode and the liquid crystal layer, and thereverse electric field Vrev has caused an after-image during display.The generation of the above-mentioned reverse electric field has beenreported in "Switching characteristic of SSFLC" by Akio Yoshida,"Preprint for Liquid Crystal Forum, October 1987" p.p. 142-143.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide aferroelectric liquid crystal device having solved the above-mentionedproblems, particularly a ferroelectric liquid crystal device whichprovides a large tilt angle of a chiral smectic liquid crystal in anon-helical structure and provides a display capable of displaying ahigh-contrast image and yet free from after-image.

According to a principal aspect of the present invention, there isprovided a liquid crystal device, comprising: a pair of substrates and achiral smectic liquid crystal disposed between the substrates; at leastone of said pair of substrates having thereon an alignment filmcomprising a polyimide which has a fluorine-containing substituent inits diamine-originated moiety.

The above-mentioned diamine originated moiety may preferably be onerepresented by the following structural formula (I) or (II). ##STR1##wherein R₁₁ denotes an arylene group, such as phenylene, naphthylene orbiphenylene which may have a substituent, e.g., an alkyl group, such asmethyl, ethyl or propyl; an alkoxy group, such as methoxy, ethoxy orpropoxy; or a halogen atom, such as fluorine, chlorine or bromine;##STR2## wherein R₂₁ denotes ##STR3## or --SO₂ --; and R₂₂, R₂₃ and R₂₄respectively denote --CF₃, --CH₃ or --H with proviso that at least oneof R₂₁ -R₂₄ is a fluorine-containing substituent.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic sectional view of an embodiment of the liquidcrystal device according to the present invention and FIG. 1B is aschematic plan view illustrating rubbing axes provided to a pair ofsubstrates.

FIG. 2 is a perspective view showing schematically an alignment of achiral smectic liquid crystal having a helical structure. FIG. 3 is aperspective view showing schematically an alignment state of a chiralsmectic liquid crystal having a non-helical structure.

FIG. 4A is a schematic sectional view showing an alignment state of achiral smectic liquid crystal aligned according to the presentinvention; FIG. 4B is an illustration of C-director alignments in auniform alignment state; and FIG. 4C is an illustration of C-directoralignments in a splay alignment state.

FIGS. 5A and 5B are plan views illustrating tilt angles θ in a uniformalignment state and a splay alignment state, respectively.

FIG. 6 is a sectional view showing a charge distribution, a direction ofa spontaneous polarization P_(S) and a direction of a reverse electricfield Vrev.

FIG. 7 is a schematic plan view illustrating changes in tilt angle θduring and after application of an electric field.

FIGS. 8 and 9 are graphs showing optical response characteristicsaccording to a conventional device and the present invention,respectively.

FIG. 10 is a waveform diagram illustrating driving waveforms used in anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is a schematic sectional view of an embodiment of the liquidcrystal device according to the present invention.

The liquid crystal device comprises a pair of substrates (glass plates)11a and 11b which are coated with transparent electrodes 12a and 12b ofIn₂ O₃, ITO (indium tin oxide), etc., 200-1000 Å-thick insulating films13a of SiO₂, TiO₂, Ta₂ O₅, etc., and 50-1000 Å-thick alignment controlfilms 14a and 14b of the above-mentioned fluorine-containing polyimide.

In this instance, the alignment control films 14a and 14b have beentreated by rubbing in directions which are parallel to each other and inthe same direction (indicated by arrows A in FIG. 1A). A chiral smecticliquid crystal 15 is disposed between the substrates 11a and 11b, andthe spacing between the substrates 11a and 11b is set to provide theliquid crystal layer 15 with a thickness (e.g., 0.1-3 microns) which issufficiently small to suppress the formation of a helical structure ofthe chiral smectic liquid crystal 15 by disposing spacer beads 16 of,e.g., silica, alumina, etc. between the substrates 11a and 11b, wherebythe chiral smectic liquid crystal 15 assumes a bistable alignment state.

According to our experiments, by using an alignment method using aspecific polyimide alignment film treated by rubbing as explained withreference to Examples described hereinafter, there has been realized analignment state which provides a large optical contrast between a brightand a dark state, particularly with respect to non-selected pixelsduring multiplexing drive as disclosed in U.S. Pat. No. 4,655,561, etc.,and also is free from a delay in optical response leading to a problemof after-image in a display at the time of switching during suchmultiplexing drive.

The fluorine-containing polyimide film used in the present invention maybe obtained by synthesizing a polyamide acid through condensationreaction between a carboxylic acid anhydride and a fluorine-containingdiamine and subjecting the polyamide acid to cyclization under heating.

Examples of the fluorine-containing diamine suitably used in the presentinvention may include the following: ##STR4##

Examples of the tetracarboxylic acid anhydride may include: pyromelliticanydride, 2,3,6,7-naphthalenetetracarboxylic anhydride,3,3',4,4'-diphenyltetracarboxylic anhydride,1,2,5,6-naphthalenetetracarboxylic anhydride,2,2',3,3'-diphenyltetracarboxylic anhydride,thiophene-2,3,4,5-tetracarboxylic anhydride,2,2-bis(3,4-biscarboxyphenyl)propane anhydride, 3,4-dicarboxyphenylsulfone anhydride, perylene-3,4,9,10-tetracarboxylic anhydride,bis(3,4-dicarboxyphenyl) ether anhydride, and3,3,4,4'-benzophenonetetracarboxylic anhydride. In addition to theabove, anhydrides of the following fluorine-containing tetracarboxylicacids may also be suitably or even preferably be used;2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane,2,2-bis(3-4-dicarboxyphenyl)hexafluoropropane,bis(3,4-dicarboxyphenyl)hexafluoropropane,4,4'-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane,(trifluoromethyl)pyromellitic acid, bis(trifluoromethyl)pyromelliticacid, 5,5'-bis-(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl,2,2',5,5'-tetrakis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl,5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxydiphenyl ether,5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybenzophenone,bis[(trifluoromethyl)dicarboxyphenoxy]benzene,bis[(trifluoromethyl)dicarboxyphenoxy]biphenyl,bis[(trifluoromethyl)dicarboxyphenoxy](trifluoromethyl)-benzene,bis[(trifluoromethyl)dicarboxyphenoxy]bis-(trifluoromethyl)biphenyl,bis[(trifluoromethyl)-dicarboxyphenoxy]diphenyl ether,bis(dicarboxyphenoxy)-(trifluoromethyl)benzene,bis(dicarboxyphenoxy)-bis-(trifluoromethyl)benzene,bis(dicarboxyphenoxy)-tetrakis(trifluoromethyl)benzene,bis(dicarboxyphenoxy)-bis(trifluoromethyl)biphenyl,bis(dicarboxyphenoxy)-tetrakis(trifluoromethyl)biphenyl,2,2-bis[4-(2,3-dicarboxybenzoyloxy)phenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxybenzoyloxy)-3-bromophenyl]-hexafluoropropane,2,2-bis[4-(3,4-dicarboxybenzoyloxy)-3,5-dimethylphenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]octafluorobutane,2,2-bis[(4-(2-trifluoromethyl-3,4-dicarboxybenzoyloxy)-phenyl]hexafluoropropane,1,3-bis[4-(3,4-dicarboxy-benzoyloxy)phenyl]hexafluoropropane,1,5-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]decafluoropentane,1,6-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]dodecafluorohexane,1,7-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]-tetradecafluoroheptane,1,5-bis[4-(3,4-dicarboxybenzoyloxy)-3,5-dibromophenyl]decafluoropentane,1,5-bis[4-(3,4-dicarboxybenzoyloxy)-3,5-bistrifluoromethylphenyl]decafluoropentane,1,5-bis[4-(2-trifluoromethyl-3,5-dicarboxybenzoyloxy)phenyl]decafluoropentane,2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]-hexafluoropropane,2,2-bis[4-(2,3-dicarboxyphenoxy)-phenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxyphenoxy)-3-bromophenyl]hexafluoropropane,2,2-bis(4-(3,4-dicarboxyphenoxy)-3,5-dibromophenyl]-hexafluoropropane,2,2-bis[4-(3,4-dicarboxyphenoxy)-3,5-dimethylphenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]octafluorobutene,2,2-bis[4-(3,4-dicarboxy-2-trifluoromethylphenoxy)phenyl]-hexafluoropropane,1,3-bis[4-(3,4-dicarboxy-phenoxy)phenyl]hexafluoropropane,1,5-bis[4-(3,4-dicarboxyphenoxy)-phenyl]decafluoropentane,1,6-bis[4-(3,4-dicarboxyphenoxy)phenyl] dodecafluorohexane,1,7-bis-[4-(3,4-dicarboxyphenoxy)phenyl]tetradecafluoropentane,1,5-bis[4-(3,4-dicarboxyphenoxy)-3,5-dibromophenyl]decafluoropentane,1,5-bis[4-(3,4-dicarboxyphenoxy)-3,5-bistrifluoromethylphenyl]decafluoropentane,and1,5-bis[4-(3,4-dicarboxy-2-trifluoromethylphenoxy)phenyl]decafluoropentane.

According to another preferred embodiment of the present invention, thealignment films 14a and 14b may comprise a polyimide which has at leastone structural unit represented by the following formula (III)-(VI) andin combination with a structural unit represented by the followingformula (VII): ##STR5##

The above polyimide may be obtained by synthesizing a polyamide acidthrough condensation of a carboxylic anhydride and a diamine andcyclizing the polyamide under heating. More specifically, a polyamideacid may be prepared by reacting at least one of the followingtetarcarboxylic anhydrides (1)-(4): ##STR6## with the followingfluorine-containing diamine (5): ##STR7## Then, the polyamide acid mayafter dilution with an appropriate solvent as desired, be applied onto asubstrate and then cured under heating to provide a polyimide film.

The tetracarboxylic anhydride represented by any one of the formulas(1)-(4) may be used in a proportion of 0.01-100 wt. parts, preferably0.1-10 wt. parts, per 1 wt. part of the diamine (5). The compoundsrepresented by the formulas (1)-(4) may be used singly or in combinationof two or more species. It is particularly suitable to use thecarboxylic anhydride of the formula (4) for preparing the polyimidefilms. When two or more of the compounds (1) -(4) are used incombination, it is preferred that they are used in substantially thesame amounts.

In order to form a film of the polyimide on a substrate, a solution of apolyamide acid as a precursor of the polyimide in a solvent, such asdimethylformamide, dimethylacetoamide, dimethylsulfoxide orN-methylpyrrolidone at a concentration of 0.01-40 wt. % may be appliedonto the substrate by spinner coating, spray coating, roller coating,etc., and heated at 100-350° C., preferably 200-300° C., to causedehydro-cyclization. The thus-formed polyimide film may be rubbed with acloth, etc. The polyimide film may be formed in a thickness of, e.g., 30Å-1 micron, preferably 200-2000 Å, so as to also function as aninsulating film. In this case, the insulating films 13a and 13b can beomitted. Further, in case of forming the polyimide film on theinsulating film 13a or 13b, the polyimide film thickness may be set to200 Å or less, preferably 100 Å or less.

The liquid crystal material used in the present invention may preferablybe one showing a phase transition from isotropic phase throughcholesteric phase and smectic A phase into chiral smectic C phase in thecourse of temperature decrease. Particularly, a chiral smectic liquidcrystal showing a helical pitch of 0.8 microns or longer in cholestericphase (measured at a mid temperature in the cholesteric range).Preferred examples of such a liquid crystal material may include liquidcrystal materials (1)-(5) below comprising the following liquid crystals"LC-1", "80B" and "80SI*" in the indicated proportions by weight.##STR8##

Liquid crystal material

(1) (LC-1)₉₀ /(80B)₁₀

(2) (LC-1)₈₀ /(80B)₂₀

(3) (LC-1)₇₀ (80B)₃₀

(4) (LC-1)₆₀ /(80B)₄₀

(5) (80SI*)₁₀₀

FIG. 1B is a schematic plan view for illustrating another preferredembodiment of the liquid crystal device according to the presentinvention. The device comprises a pair of substrates including onesubstrate closer to a viewing position having a rubbing axis provided inthe direction of an arrow 2A and the other substrate farther from theviewing position having a rubbing axis in the direction of an arrow 2Bwhich intersects with the rubbing axis 2A at an intersection angle inthe range of 2-15 degrees, preferably 3-12 degrees. In a particularlypreferred embodiment, the rubbing axis 2A is disposed to form anintersection angle θx in the counter-clockwise direction with respect tothe rubbing axis 2B.

FIG. 2 is a schematic illustration of a ferroelectric liquid crystalcell (device) for explaining operation thereof. Reference numerals 21aand 21b denote substrates (glass plates) on which a transparentelectrode of, e.g., In₂ O₃, SnO₂, ITO (indium-tin-oxide), etc., isdisposed, respectively. A liquid crystal of an SmC*-phase (chiralsmectic C phase) or SmH*-phase (chiral smectic H phase) in which liquidcrystal molecular layers 22 are aligned perpendicular to surfaces of theglass plates is hermetically disposed therebetween. Full lines 23 showliquid crystal molecules. Each liquid crystal molecule 23 has a dipolemoment (P⊥) 24 in a direction perpendicular to the axis thereof. Theliquid crystal molecules 23 continuously form a helical structure in thedirection of extension of the substrates. When a voltage higher than acertain threshold level is applied between electrodes formed on thesubstrates 21a and 21b, a helical structure of the liquid crystalmolecule 23 is unwound or released to change the alignment direction ofrespective liquid crystal molecules 23 so that the dipole moment (P⊥) 24are all directed in the direction of the electric field. The liquidcrystal molecules 23 have an elongated shape and show refractiveanisotropy between the long axis and the short axis thereof.Accordingly, it is easily understood that when, for instance, polarizersarranged in a cross nicol relationship, i.e., with their polarizingdirections crossing each other, are disposed on the upper and the lowersurfaces of the glass plates, the liquid crystal cell thus arrangedfunctions as a liquid crystal optical modulation device of which opticalcharacteristics vary depending upon the polarity of an applied voltage.

Further, when the liquid crystal cell is made sufficiently thin (e.g.,0.1-3 microns), the helical structure of the liquid crystal molecules isunwound to provide a non-helical structure even in the absence of anelectric field, whereby the dipole moment assumes either of the twostates, i.e., Pa in an upper direction 34a or Pb in a lower direction34b as shown in FIG. 3, thus providing a bistable condition. When anelectric field Ea or Eb higher than a certain threshold level anddifferent from each other in polarity as shown in FIG. 3 is applied to acell having the above-mentioned characteristics, the dipole moment isdirected either in the upper direction 34a or in the lower direction 34bdepending on the vector of the electric field Ea or Eb. Incorrespondence with this, the liquid crystal molecules are oriented ineither of a first stable state 33a and a second stable state 33b.

A first advantage attained by using such a ferroelectric liquid crystalcell is that the response speed is quite fast, and a second advantage isthat the orientation of the liquid crystal shows bistability. The secondadvantage will be further explained, e.g., with reference to FIG. 3.When the electric field Ea is applied to the liquid crystal molecules,they are oriented in the first stable state 33a. This state is stablyretained even if the electric field is removed. On the other hand, whenthe electric field Eb of which direction is opposite to that of theelectric field Ea is applied thereto, the liquid crystal molecules areoriented to the second stable state 33b, whereby the directions ofmolecules are changed. This state is similarly stably retained even ifthe electric field is removed. Further, as long as the magnitude of theelectric field Ea or Eb being applied is not above a certain thresholdvalue, the liquid crystal molecules are placed in the respectiveorientation states.

FIG. 4A is a schematic sectional view showing an alignment state ofliquid crystal molecules attained by the present invention, and FIG. 4Bis a view showing alignment of corresponding C-directors.

Reference numerals 61a and 61b in FIG. 4A denote upper and lowersubstrates, respectively. Numeral 60 denotes a molecular layer composedof liquid crystal molecules 62, and liquid crystal molecules 62 arealigned so as to change their positions along the bottom face 64(circular) of a cone 64. FIG. 4B more specifically shows a change inC-directors. Referring to FIG. 4B, at U₁ are shown C-directors 81 (eachbeing a projection of a molecular long axis onto an imaginary planeperpendicular to the normal to a molecular layer 60) in one stableorientation state, and at U₂ are shown C-directors 81 in the otherstable orientation state.

On the other hand, an alignment state attained by a conventionalrubbing-treated polyimide film may be represented by a C-directordiagram of FIG. 4C, which shows an alignment state wherein molecularaxes are twisted in a large degree from the upper substrate 61a to thelower substrate 61b to provide a smaller tilt angle θ.

FIG. 5A is a schematic plan view illustrating a tilt angle θ in analignment state where C-directors 81 assume a state shown in FIG. 4B(referred to as "uniform alignment state"), and FIG. 5B is a schematicplan view illustrating a tilt angle θ in an alignment state whereC-directors 81 assume a state shown in FIG. 4C (referred to as "splayalignment state"). In these figures, reference numeral 50 denotes arubbing axis provided to the abovementioned fluorine-containingpolyimide film, numeral 51a denotes an average molecular axis in theorientation state U₁, numeral 51b denotes an average molecular axis inthe orientation state U₂, numeral 52a denotes an average molecular axisin the orientation state S₁, and numeral 52b denotes an averagemolecular axis in the orientation state S₂. The average molecular axes51a and 51b can be switched to each other by applying voltages ofmutually opposite polarities. Similar switching is caused between theaverage molecular axes 52a and 52b.

Next, the effectiveness of the uniform alignment state with respect to adelay in optical response (after-image) due to a reverse electric fieldVrev is explained.

If the capacitance of an insulating layer constituting a liquid crystalcell is denoted by Ci, the capacitance of a liquid crystal layer isdenoted by C_(LC) and the spontaneous polarization of the liquid crystalis denoted by P_(S), Vrev causing after-image is expressed by thefollowing equation.

    Vrev=2P.sub.S /(Ci+C.sub.LC)

FIG. 6 is a schematic sectional view illustrating changes in chargedistribution direction of P_(S) and direction of the reverse electricfield in a liquid crystal cell. At FIG. 6(a), there is shown adistribution of ⊕ and ⊖ charges in a memory state before application ofa pulse electric field, where the spontaneous polarization is directedfrom ⊕ charges to ⊖ charges. At FIG. 6(b) is shown state immediatelyafter removal of a pulse electric field, when the direction of thespontaneous polarization P_(S) is opposite to that shown at FIG. 6(a)(thus, the liquid crystal molecules are inverted from one stableorientation state to the other orientation state) but the distributionof the ⊖ and ⊕ charges is similar to that shown at FIG. 6(a), so that areverse electric field Vrev is generated as indicated by an arrow shownat FIG. 6(b). The reverse electric field Vrev disappears in a short timeto provide a distribution of ⊖ and ⊕ charges as shown at FIG. 6(c).

FIG. 7 is a plan view showing a change in optical response in a splayalignment state given by a conventional polyimide alignment film interms of a change in tilt angle θ. Referring to FIG. 7, at the time ofapplication of a pulse electric field, the orientation of liquid crystalmolecules is changed from an average molecular axis S(A) in a splayalignment state to be overshot to an average molecular axis U₂ in auniform alignment state close to that providing a maximum tilt angle Halong a path denoted by an arrow X₁, and immediately after the removalof the pulse electric field, the orientation is changed along a pathdenoted by an arrow X₂ to an average molecular axis S(B) in a splayalignment state providing a decreased tilt angle θ due to the action ofthe reverse electric field Vrev shown at FIG. 6(b). Then, as the reverseelectric field Vrev attenuates as shown at FIG. 6(c), the orientation ischanged along a path denoted by an arrow X₃ to an average molecular axisS(C) in a splay alignment state providing a stable orientation statehaving a somewhat increased tilt angle θ.

In the alignment state given by using the above-mentionedfluorine-containing polyimide film of the present invention, the averagemolecular axes S(A), S(B) and S(C) in the splay alignment state shown inFIG. 7 are not caused but it is possible to form an alignment state withan average molecular axis giving a tilt angle 0 which is close to amaximum tilt angle H. An optical response at this time according to thepresent invention is shown in FIG. 9. FIG. 9 shows that a delay inoptical response causing after-image is obviated and a high contrast inmemory states is caused.

Hereinbelow, the present invention will be explained based on Examples.

EXAMPLE 1

Two 1.1 mm-thick glass plates each provided with a 1000 Å-thick ITO filmwere respectively coated with a 3.0 wt. % solution of a polyamide acidrepresented by the formula shown below in a mixture solvent ofN-methylpyrrolidone/n-butylcellosolve=5/1 by means of a spinner rotatingat 3000 rpm for 30 min. ##STR9## After the coating, the film wassubjected to curing under heating at 250° C. for about an hour to form a450 Å-thick film. The coating film was then rubbed in one direction witha nylon-planted cloth.

On one of the two glass plates thus treated, 1.5 microns alumina beadswere dispersed, and the other glass plate was superposed thereon so thattheir rubbing axes were parallel to each other and disposed in the samedirection to form a blank cell.

The blank cell was filled with a ferroelectric smectic liquid crystal("CS-1014" (trade name), available from Chisso K.K.) under vacuum and,after sealing, was gradually cooled from isotropic phase at a rate of 5°C./hour to 30° C., whereby an alignment was effected. The "CS-1014"liquid crystal in the cell showed the following phase transition series.##STR10##

The experiment thereafter was performed at 25° C.

The above-prepared liquid crystal cell was sandwiched between a pair of90 degrees-cross nicol polarizers to provide a liquid crystal device andwas supplied with a pulse of 50 usec and 30 V. Then, the cross nicolpolarizers were set at the extinction position (providing the darkeststate), and the transmittance through the liquid crystal device at thistime was measured by a photo-multiplier. Then, a pulse of 50 μsec and-30 V was applied to the device, and the transmittance (brightest state)at this time was measured in the same manner, whereby the following datawere obtained.

Tilt angle θ=15 degrees, transmittance in the brightest state=42%,transmittance in the darkest state=1%, contrast ratio=42:1.

The delay in optical response causing after-image was 0.2 sec or less.

The liquid crystal device was subjected to multiplexing drive fordisplay using driving waveforms shown in FIG. 10, whereby a high-qualitydisplay with a high contrast was attained. Further, after an imagedisplay of a prescribed character image, the whole picture area waserased into "white", whereby no after-image was recognized. Referring toFIG. 10, at S_(N), S_(N+1) and S_(N+2) are shown voltage waveformsapplied to scanning lines, at I is shown a voltage waveform applied to arepresentative date line, and at (I-S_(N)) is shown a combined voltagewaveform applied to the data line I and the scanning line S_(N). In theabove embodiment, the drive was performed under the conditions of V₀=5-8 volts and T=20-70 μsec.

Examples 2-20

Liquid crystal cells were prepared in the same manner as in Example 1except that the alignment control films (in terms of precursor polyamideacids represented by the formulas) and liquid crystal materials shown inTable 1 below were used.

The respective cells were tested in the same manner as in Example 1,whereby measured data of contrast ratio and delay time in opticalresponse shown in Table 2 appearing hereinafter were obtained.

The respective cells were subjected to the multiplexing drive fordisplay in the same manner as in Example 1, whereby similar results wereattained with respect to contrast and after-image.

                                      TABLE 1                                     __________________________________________________________________________    Example                                                                            Alignment film (precursor polyamide acid)    Liquid crystal              __________________________________________________________________________                                                      material                          ##STR11##                                   "CS1014" (trade name)                                                         (FLC, Chisso K.K.)               (n = 700-2000)                                                           3                                                                                   ##STR12##                                   " CS1014" (trade name)                                                        (FLC, Chisso K.K.)               (n = 700-2000)                                                           4                                                                                   ##STR13##                                   "CS1014" (trade name)                                                         (FLC, Chisso K.K.)               (n = 700-2000)                                                           5    "                                            Liquid crystal                                                                material (3) described                                                        hereinbefore                6                                                                                   ##STR14##                                   Liquid crystal material                                                       (3) described hereinbefo                                                      re                               (n = 700-2000)                                                           7                                                                                   ##STR15##                                   "CS-1014" (trade name)                                                        (FLC, Chisso K.K.)               (n = 700-2000)                                                           8                                                                                   ##STR16##                                   "CS-1014"  (trade name)                                                       FLC, Chisso K.K.)                (n = 700-2000)                                                           9                                                                                   ##STR17##                                   "CS-1014" (trade name)                                                        (FLC, Chisso K.K.)               (n = 700-2000)                                                           10                                                                                  ##STR18##                                   "CS-1014" (trade name)                                                        (FLC, Chisso K.K.)               (n = 700-2000)                                                           11   "                                            Liquid crystal                                                                material (3)                12                                                                                  ##STR19##                                   Liquid crystal material                                                       (3)                              (n = 700-2000)                                                           13                                                                                  ##STR20##                                   Liquid crystal material                                                       (3)                               ##STR21##                                                                    (n = 700-2000)                                                           14                                                                                  ##STR22##                                   "CS-1014" (trade name)                                                        (FLC, Chisso K.K.)                ##STR23##                                                                    (n = 700-2000)                                                           15                                                                                  ##STR24##                                   "CS-1014" (trade name)                                                        (FLC, Chisso K.K.)               n = 700-2000)                                                            16                                                                                  ##STR25##                                   "CS-1014" (trade name)                                                        (FLC, Chisso K.K.)               (n = 700-2000)                                                           17                                                                                  ##STR26##                                   "CS-1014" (trade name)                                                        (FLC, Chisso K.K.)               (n = 700-2000)                                                           18   "                                            Liquid crystal                                                                material (3)                19                                                                                  ##STR27##                                   Liquid crystal material                                                       (3)                              (n = 700-2000)                                                           20                                                                                  ##STR28##                                   Liquid crystal material                                                       (3)                               ##STR29##                                                                    (n = 700-2000)                                                           __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        Example  Contrast ratio                                                                           Delay in optical response (sec)                           ______________________________________                                         2       45:1       0.3                                                        3       42:1       0.1                                                        4       51:1       0.2                                                        5       39:1       0.3                                                        6       31:1       0.1                                                        7       49:1       0.2                                                        8       42:1       0.2                                                        9       39:1       0.1                                                       10       50:1       0.1                                                       11       40:1       0.1                                                       12       42:1       0.2                                                       13       52:1       0.1                                                       14       40:1       0.2                                                       15       31:1       0.2                                                       16       42:1       0.3                                                       17       29:1       0.2                                                       18       35:1       0.1                                                       19       23:1       0.1                                                       20       24:1       0.1                                                       ______________________________________                                    

Comparative Examples 1-4

Liquid crystal cells were prepared in the same manner as in Example 1except that the alignment control films (in terms of commerciallyavailable precursor polyamide acid varnish, the degree of polymerizationbeing each in the range of 700-2000) and liquid crystal materials shownin Table 3 below were used. The measured data of contrast ratio anddelay in optical response measured for each of the cells are shown inTable 4 below.

The respective cells were subjected to the multiplexing drive fordisplay in the same manner as in Example 1, whereby the resultantcontrasts were smaller than that given by Example 1 and after-image wasrecognized for each cell.

                  TABLE 3                                                         ______________________________________                                        Comparative                                                                            Alignment film   Liquid crystal                                      Example  (polyamide acid varnish)                                                                       material                                            ______________________________________                                        1        "SP-710" (trade name)                                                                          "CS-1014" (trade                                             (aromatic polyimide                                                                            name) (FLC, Chisso                                           varnish, Toray K.K.)                                                                           K.K.)                                               2        ditto            Liquid crystal                                                                material (3) described                                                        hereinbefore                                        3        "LQ-5200" (trade name)                                                                         "CS-1014"                                                    (polyimide varnish,                                                           Hitachi Kasei K.K.)                                                  4        ditto            Liquid crystal material                                                       (3)                                                 ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Comp. Example                                                                           Contrast ratio                                                                           Delay in optical response (sec)                          ______________________________________                                        1         8:1        1.5                                                      2         7:1        2.5                                                      3         10:1       1.2                                                      4         8:1        2.2                                                      ______________________________________                                    

Examples 21-40

Liquid crystal cells were prepared in the same manner as in Example1-48, respectively, except that a pair of substrates for each cell weredisposed so that their rubbing axes intersected each other at acounter-clockwise intersection angle of -6 degrees as shown in FIG. 1B.

The respective cells prepared above were tested in the same manner as inExamples 1-20, respectively, whereby measured data shown in Table 5below were obtained, showing remarkably improved contrast ratioscompared with the corresponding cells of Examples 1-20.

                  TABLE 5                                                         ______________________________________                                                                         Delay in optical                             Example Polyimide    Contrast ratio                                                                            response (sec)                               ______________________________________                                        21      Same as Ex. 1                                                                              43:1        0.2                                          22      Same as Ex. 2                                                                              46:1        0.2                                          23      Same as Ex. 3                                                                              45:1        0.1                                          24      Same as Ex. 4                                                                              56:1        0.2                                          25      Same as Ex. 5                                                                              47:1        0.2                                          26      Same as Ex. 6                                                                              48:1        0.1                                          27      Same as Ex. 7                                                                              50:1        0.2                                          28      Same as Ex. 8                                                                              46:1        0.2                                          29      Same as Ex. 9                                                                              41:1        0.1                                          30      Same as Ex. 10                                                                             50:1        0.1                                          31      Same as Ex. 11                                                                             45:1        0.1                                          32      Same as Ex. 12                                                                             44:1        0.2                                          33      Same as Ex. 13                                                                             52:1        0.1                                          34      Same as Ex. 14                                                                             42:1        0.2                                          35      Same as Ex. 15                                                                             37:1        0.2                                          36      Same as Ex. 16                                                                             45:1        0.2                                          37      Same as Ex. 17                                                                             35:1        0.2                                          38      Same as Ex. 18                                                                             41:1        0.1                                          39      Same as Ex. 19                                                                             38:1        0.1                                          40      Same as Ex. 20                                                                             43:1        0.1                                          ______________________________________                                    

Comparative Examples 5-8

Liquid crystal cells were prepared in the same manner as in Example 21except that the alignment control films (in terms of commerciallyavailable precursor polyamide acid varnish, the degree of polymerizationbeing each in the range of 700-2000) and liquid crystal materials shownin Table 6 below were used. The measured data of contrast ratio anddelay in optical response measured for each of the cells are shown inTable 7 below.

The respective cells were subjected to the multiplexing drive fordisplay in the same manner as in Example 1, whereby the resultantcontrasts were smaller than that given by Example 21 and after-image wasrecognized for each cell.

                  TABLE 6                                                         ______________________________________                                        Comparative                                                                            Alignment film   Liquid crystal                                      Example  (polyamide acid varnish)                                                                       material                                            ______________________________________                                        5        "SP-710" (trade name)                                                                          "CS-1014" (trade                                             (aromatic polyimide                                                                            name) (FLC, Chisso                                           varnish, Toray K.K.)                                                                           K.K.)                                               6        ditto            Liquid crystal                                                                material (3) described                                                        hereinbefore                                        7        "LQ-5200" (trade name)                                                                         "CS-1014"                                                    (polyimide varnish,                                                           Hitachi Kasei K.K.)                                                  8        ditto            Liquid crystal material                                                       (3)                                                 ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Comp. Example                                                                           Contrast ratio                                                                            Delay in optical response (sec)                         ______________________________________                                        5         9:1         1.5                                                     6         7:1         2.5                                                     7         11:1        1.2                                                     8         7:1         2.2                                                     ______________________________________                                    

As is apparent from the above Examples and Comparative Examples,according to the present invention, there is obtained a liquid crystaldevice which provides a high-quality display including a high contrastbetween the bright and dark states, particularly a very large displaycontrast at the time of multiplexing drive and is free from uglyafter-image.

What is claimed is:
 1. A liquid crystal device, comprising:a pair ofsubstrates and a chiral smectic liquid crystal disposed between thesubstrates, said pair of substrates being disposed to have a spacingsmall enough to suppress the formation of a helical alignment structureof the chiral smectic liquid crystal; wherein at least one of said pairof substrates has thereon an alignment film comprising a polyimide whichhas a fluorine-containing substituent in its diamine-originated moiety.2. A device according to claim 1, wherein said fluorine-containingsubstituent is a fluoroalkyl group.
 3. A device according to claim 1,wherein said diamine-originated moiety comprises a recurring unitrepresented by the following structural formula (I): ##STR30## whereinR₁₁ denotes an arylene group which may have a substituent.
 4. A deviceaccording to claim 1, wherein said diamine-originated moiety comprises arecurring unit represented by the following structural formula (II):##STR31## wherein R₂₁ denotes ##STR32## or --SO₂ --; and R₂₂, R₂₃ andR₂₄ respectively denote --CF₃, --CH₃ or --H with proviso that at leastone of R₂₁ -R₂₄ is a fluorine-containing substituent.
 5. A deviceaccording to claim 1, wherein said polyimide film has been subjected toa uniaxial aligning treatment.
 6. A device according to claim 5, whereinsaid uniaxial aligning treatment is rubbing.
 7. A device according toclaim 5, wherein said polyimide film subjected to a uniaxial aligningtreatment overlies an insulating film which overlies an electrode whichis disposed on a substrate.
 8. A device according to claim 7, whereinsaid polyimide film has a thickness of 50-1000 Å, and said insulatingfilm has a thickness of 200-1000 Å.
 9. A device according to claim 7,wherein said polyimide film has a thickness of 100 Å or less.
 10. Adevice according to claim 1, wherein said chiral smectic liquid crystalhas been cooled from a temperature higher than a range giving smectic Aphase to form at least two different stable orientation states.
 11. Aliquid crystal device, comprising: a pair of substrates and a chiralsmectic liquid crystal disposed between the substrates, said substratesbeing disposed to have a spacing small enough to suppress the formationof a helical alignment structure of the chiral smectic liquid crystal;at least one of said pair of substrates having thereon an alignment filmcomprising a polyimide which has at least one structural unitrepresented by the following formula (III)-(VI) and also a structuralunit represented by the following formula (VII): ##STR33##
 12. A deviceaccording to claim 11, wherein said polyimide film has been subjected toa uniaxial aligning treatment.
 13. A device according to claim 11,wherein said uniaxial aligning treatment is rubbing.
 14. A deviceaccording to claim 11, wherein said polyimide film subjected to auniaxial aligning treatment overlies an insulating film which overliesan electrode which is disposed on a substrate.
 15. A device according toclaim 14, wherein said polyimide film has a thickness of 50-1000 Å, andsaid insulating film has a thickness of 200-1000 Å.
 16. A deviceaccording to claim 14, wherein said polyimide film has a thickness of100 Å or less.
 17. A device according to claim 11, wherein said chiralsmectic liquid crystal has been cooled from a temperature higher than arange giving smectic A phase to form at least two different stableorientation states.
 18. A liquid crystal device, comprising:a pair ofsubstrates and a chiral smectic liquid crystal disposed between thesubstrates, said pair of substrates being disposed to have a spacingsmall enough to suppress the formation of a helical alignment structureof the chiral smectic liquid crystal; wherein at least one of said pairof substrates has thereon an alignment film comprising a polyimide whichhas a fluorine-containing substituent in both its diamine-originatedmoiety and carboxylic acid-originated moiety.
 19. A device according toclaim 18, wherein said fluorine-containing substituent is a fluoroalkylgroup.
 20. A device according to claim 18, wherein said carboxylicacid-originated moiety has been derived from a fluorine-containingtetracarboxylic acid anhydride.
 21. A device according to claim 20,wherein said fluorine-containing tetracarboxylic acid is selected fromthe group consisting of:2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane,2,2-bis(3-4-dicarboxyphenyl)hexafluoropropane,bis(3,4-dicarboxyphenyl)hexafluoropropane,4,4'-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane,(trifluoromethyl)pyromellitic acid, bis(trifluoromethyl)pyromelliticacid, 5,5'-bis(trifluoromethyl)- 3,3',4,4'-tetracarboxybiphenyl,2,2',5,5'-tetrakis-(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl,5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxydiphenyl ether,5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybenzophenone,bis[(trifluoromethyl)dicarboxyphenoxy]benzene,bis[(trifluoromethyl)dicarboxyphenoxy]biphenyl,bis[(trifluoromethyl)dicarboxyphenoxy](trifluoromethyl)benzene,bis[(trifluoromethyl)dicarboxyphenoxy)bis(trifluoromethyl)biphenyl,bis[(trifluoromethyl)dicarboxyphenoxy]diphenyl ether,bis(dicarboxyphenoxy)(trifluoromethyl)benzene,bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene,bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene,bis(dicarboxypenoxy)bis(trifluoromethyl)biphenyl,bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)biphenyl,2,2-bis[4-(2,3-dicarboxybenzoyloxy)phenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxybenzoyloxy)-3-bromophenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxybenzoyloxy)-3,5-dimethylphenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]-octafluorobutane,2,2-bis[(4-(2-trifluoromethyl-3,4-dicarboxybenzoyloxy)phenyl]hexafluoropropane,1,3-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]hexafluoropropane,1,5-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]-decafluoropentane,1,6-bis[4-(3,4-dicarboxybenzoyloxy)-phenyl]dodecafluorohexane,1,7-bis[4-(3,4-dicarboxybenzoyloxy)phenyl]tetradecafluoroheptane,1,5-bis[4-(3,4-dicarboxybenzoyloxy)-3,5-dibromophenyl]decafluoropentane,1,5-bis[4-(3,4-dicarboxybenzoyloxy)-3,5-bistrifluoromethylphenyl]decafluoropentane,1,5-bis[4-(2-trifluoromethyl-3,5-dicarboxybenzoyloxy)phenyl]-decafluoropentane,2,2-bis[4-(3,4-dicarboxyphenoxy)-phenyl]hexafluoropropane,2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxyphenoxy)-3-bromophenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxyphenoxy)-3,5-dibromophenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxyphenoxy)-3,5-dimethylphenyl]hexafluoropropane,2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]octafluorobutene,2,2-bis[4-(3,4-dicarboxy-2-trifluoromethylphenoxy)phenyl]hexafluoropropane,1,3-bis[4-(3,4-dicarboxyphenoxy)-phenyl]hexafluoropropane,1,5-bis[4-(3,4-dicarboxyphenoxy)phenyl]decafluoropentane,1,6-bis[4-(3,4- dicarboxyphenoxy)phenyl]dodecafluorohexane,1,7-bis-[(4-(3,4-dicarboxyphenoxy)phenyl]tetradecafluoropentane,1,5-bis[4-(3,4-dicarboxyphenoxy)-3,5-dibromophenyl]-decafluoropentane,1,5-bis[4-(3,4-dicarboxyphenoxy)-4,5-bistrifluoromethylphenyl]decafluoropentane,and1,5-bis[4-(3,4-dicarboxy-2-trifluoromethylphenoxy)-phenyl]decafluoropentane.22. A device according to claim 18, wherein said carboxylicacid-originated moiety has been derived from two or more species ofcarboxylic acids.
 23. A device according to claim 18, wherein saiddiamine-originated moiety has been originated from two or more speciesof diamines.
 24. A device according to claim 18, wherein said polyimidefilm has been subjected to a uniaxial aligning treatment.
 25. A deviceaccording to claim 24, wherein said uniaxial aligning treatment isrubbing.
 26. A device according to claim 24, wherein said polyimide filmsubjected to a uniaxial aligning treatment is disposed by the medium ofan insulating film on an electrode which is in turn disposed on asubstrate.
 27. A device according to claim 26, wherein said polyimidefilm has a thickness of 50-1000 Å, and said insulating film has athickness of 200-1000 Å.
 28. A device according to claim 26, whereinsaid polyimide film has a thickness of 100 Å or less.
 29. A deviceaccording to claim 18, wherein said chiral smectic liquid crystal hasbeen cooled from a temperature higher than a range giving smectic Aphase to form at least two different stable orientation states.
 30. Aliquid crystal device, comprising:a pair of substrates and a chiralsmectic liquid crystal disposed between the substrates, said pair ofsubstrates being disposed to have a spacing small enough to suppress theformation of a helical alignment structure of the chiral smectic liquidcrystal; each substrate being coated with an alignment film comprising apolyimide which has a fluorine-containing substituent in itsdiamine-originated moiety, wherein each alignment film has beensubjected to a uniaxial aligning treatment so that the resultant pair ofalignment films have directions of the uniaxial aligning treatment whichintersect each other at an intersection angle.
 31. A device according toclaim 30, wherein said fluorine-containing substituent is a fluoroalkylgroup.
 32. A device according to claim 30, wherein said uniaxialaligning treatment is rubbing.
 33. A device according to claim 30,wherein said polyimide film subjected to a uniaxial aligning treatmentoverlies an insulating film which overlies an electrode which isdisposed on a substrate.
 34. A device according to claim 33, whereinsaid polyimide film has a thickness of 50-1000 Å, and said insulatingfilm has a thickness of 200-1000 Å.
 35. A device according to claim 33,wherein said polyimide film has a thickness of 100 Å or less.
 36. Adevice according to claim 30, wherein said polyimide film subjected to auniaxial aligning treatment is disposed by the medium of an insulatingfilm on an electrode which is disposed on each of said pair ofsubstrates, so that the resultant pair of polyimide films havedirections of the uniaxial aligning treatment which intersect each otherat an intersection angle of 2-15 degrees.
 37. A device according toclaim 36, wherein said intersection angle is 3-12 degrees.
 38. A deviceaccording to claim 30, wherein said polyimide film subjected to auniaxial aligning treatment is disposed on each of the pair ofsubstrates and the directions of the uniaxial aligning treatment axesprovided to the resultant pair of polyimide films are such that theuniaxial aligning treatment axis provided to the polyimide film disposedon one of the substrates which is closer to a viewing position isdisposed to have a counter-clockwise angle of 2-15 degrees from theuniaxial aligning treatment axis provided to the polyimide film disposedon the other of the substrates which is farther from the viewingposition.
 39. A device according to claim 38, wherein thecounter-clockwise angle is set within the range of 3-12 degrees.
 40. Adevice according to claim 30, wherein said chiral smectic liquid crystalhas been cooled from a temperature higher than a range giving smectic Aphase to form at least two different stable orientation states.
 41. Aliquid crystal device, comprising:a pair of substrates and a chiralsmectic liquid crystal arranged in a plurality of molecular layers eachcomprising a plurality of liquid crystal molecules disposed between thesubstrates; at least one of said pair of substrates having thereon analignment film comprising a polyimide which has a fluorine-containingsubstituent in its diamine-originated moiety; said molecular layers ofthe chiral smectic liquid crystal being inclined with respect to bothsubstrates and bent between the substrates.
 42. A device according toclaim 41, wherein said fluorine-containing substituent is a fluoroalkylgroup.
 43. A device according to claim 41, wherein saiddiamine-originated moiety comprises a recurring unit represented by thefollowing structural formula (I): ##STR34## wherein R₁₁ denotes anarylene group which may have a substituent.
 44. A device according toclaim 41, wherein said diamine-originated moiety comprises a recurringunit represented by the following structural formula (II): ##STR35##wherein R₂₁ denotes ##STR36## or --SO₂ --; and R₂₂, R₂₃ and R₂₄respectively denote --CF₃, --CH₃ or --H with proviso that at least oneof R₂₁ -R₂₄ is a fluorine-containing substituent.
 45. A device accordingto claim 41, wherein said polyimide film has been subjected to auniaxial aligning treatment.
 46. A device according to claim 45, whereinsaid uniaxial aligning treatment is rubbing.
 47. A device according toclaim 45, wherein said polyimide film subjected to a uniaxial aligningtreatment overlies an insulating film which overlies an electrode whichis disposed on a substrate.
 48. A device according to claim 47, whereinsaid polyimide film has a thickness of 50-1000 Å, and said insulatingfilm has a thickness of 200-1000 Å.
 49. A device according to claim 47,wherein said polyimide film has a thickness of 100 Åor less.
 50. Adevice according to claim 41, wherein said pair of substrates aredisposed to have a spacing small enough to suppress the formation of ahelical alignment structure of the chiral smectic liquid crystal.
 51. Adevice according to claim 50, wherein said chiral smectic liquid crystalhas been cooled from a temperature higher than a range giving smectic Aphase to form at least two different stable orientation states.
 52. Aliquid crystal device, comprising:a pair of substrates and a chiralsmectic liquid crustal disposed between the substrates; at least on ofsaid pair of substrates having there on an alignment film comprising apolyimide which has a fluorine-containing substituent in itsdiamine-originated moiety; said chiral smectic liquid being disposed toform a plurality of molecular layers generally perpendicular to thesubstrates, each molecular layer comprising a plurality of liquidcrystal molecules.
 53. A device according to claim 52, wherein saidfluorine-containing substituent is a fluoroalkyl group.
 54. A deviceaccording to claim 52, wherein said diamine-originated moiety comprisesa recurring unit represented by the following structural formula (I):##STR37## wherein R₁₁ denotes an arylene group which may have asubstituent.
 55. A device according to claim 52, wherein saiddiamine-originated moiety comprises a recurring unit represented by thefollowing structural formula (II): ##STR38## wherein R₂₁ denotes##STR39## or --SO₂ --; and R₂₂, R₂₃ and R₂₄ respectively denote --CF₃,--CH₃ or --H with proviso that at least one of R₂₁ -R₂₄ is afluorine-containing substituent.
 56. A device according to claim 53,wherein said polyimide film has been subjected to a uniaxial aligningtreatment.
 57. A device according to claim 56, wherein said uniaxialaligning treatment is rubbing.
 58. A device according to claim 56,wherein said polyimide film subjected to a uniaxial aligning treatmentoverlies an insulating film which overlies an electrode which isdisposed on a substrate.
 59. A device according to claim 58, whereinsaid polyimide film has a thickness of 50-1000 Å, and said insulatingfilm has a thickness of 200-1000 Å.
 60. A device according to claim 58,wherein said polyimide film has a thickness of 100 Å or less.
 61. Adevice according to claim 52, wherein said pair of substrates aredisposed to have a spacing small enough to suppress the formation of ahelical alignment structure of the chiral smectic liquid crystal.
 62. Adevice according to claim 61, wherein said chiral smectic liquid crystalhas been cooled from a temperature higher than a range giving smectic Aphase to form at least two different stable orientation states.